These findings could help develop medications as well as drug-free ways to boost brown fat activity in overweight children, according to researchers from the Joslin Diabetes Center and Children's Hospital Boston.

Being able to evaluate brown fat's activity through non-invasive PET imaging "may possibly provide insights into the treatment of childhood obesity," the study's first author, Dr. Laura Drubach, of the Children's Hospital program in nuclear medicine and molecular imaging, said in a Joslin news release.

After conducting PET scans on 172 study participants ranging in age from 5 to 21 years, the researchers detected active brown fat in 44 percent of the children. They pointed out that boys and girls had roughly the same amount.

Children aged 13 to 15 years old had the highest levels of brown fat and brown fat activity. Those with the lowest body mass index (the thinnest teens) showed the most energy-burning activity in their "good fat."

The study authors said the inverse relationship between body mass index and levels of brown fat activity -- and the increase in brown fat activity from childhood into adolescence -- suggests "good fat" may play a significant role in children's metabolism, energy balance and weight regulation.

And contrary to previous studies that showed brown fat in adults was more active in cold weather, the researchers found outdoor temperatures had no effect on brown fat in children.

The researchers concluded that their findings could help develop ways to combat obesity by boosting brown fat activity in children, such as lowering indoor temperatures in homes where obese children live. They noted, however, that more research is needed to explain whether thin children have more brown fat because they are thin or whether having more brown fat makes them thin.

"That's the billion dollar question," concluded the study's senior author, Dr. Aaron Cypess, assistant investigator and staff physician at Joslin. "But we do know that brown fat is a core component of pediatric and likely adult metabolism," he said in the news release.

The study was released online Aug. 12 in advance of publication in an upcoming print issue of The Journal of Pediatrics.

More information

The U.S. National Institutes of Health provides more information on brown fat.